The pro-fibrogenic effect of nerve growth factor on conjunctival fibroblasts is mediated by transforming growth factor-β

Background: Nerve growth factor (NGF) and nerve growth factor receptor (NGFR) expressions have been found to be increased in sub-conjunctival scarring. Objective: The aim of this study was to investigate the in vitro effects of NGF on some profibrogenic properties of human conjunctival fibroblasts. Methods: Expression of NGF, trkA^NGFR and p75^NTR on human fibroblasts grown from conjunctival biopsies and incubated for 2 or 6 days with NGF were evaluated by immunofluorescence, RT-PCR, flow cytometry and ELISA. The fibrogenic effect of NGF on conjunctival fibroblasts was investigated by evaluating their migration (wound model), proliferation ([³H]- thymidine incorporation), collagen production (³H]-proline incorporation), expression of alpha-smooth muscle actin (α-SMA) (cell surface ELISA) and contraction of 3D collagen gels. Results: NGF induced the expression of p75^NTR in the fibroblasts that constitutively expressed only trkA^NGF and increased the migration of wounded fibroblasts, but not their proliferation and collagen production. NGF induced the conversion of fibroblasts into myofibroblasts expressing α-SMA, and enhanced their contraction of a collagen matrix. Interestingly, chronic NGF treatment induced transforming growth factor-β1 (TGF-β1) production by fibroblasts, and following specific TGF-β neutralization, all the NGF-induced effects were completely abrogated. Conclusion: Our findings indicate that NGF, via TGF-β induction, is likely to be involved in the healing or fibrotic processes occurring in conjunctiva during some pathological conditions.